CKeditor 5 SimpleUploadAdapter howto?

I am trying to integrate CKeditor 5's SimpleUploadAdapter.  The plugin and config are ok, however, I am unsure how to possibly write the method to upload the image.  If I understand the plugin, I must right an uploadStuff to upload the file, for example, an image as explained here.  I wonder if someone might be able to explain how I might accomplish this.  I have search the internet for example, even in PHP, but cannot find one.  Any help appreciated.

Code:

    ClassicEditor
    .create( document.querySelector( '#post_body' ), {
        simpleUpload: {
          uploadUrl: 'https://development.example.com/uploadStuff',
        }
    } )
    .then( )
            .catch( error => {
            console.error( error );
    } );